1. Field of the Invention
The present invention relates to a radio communication apparatus and a radio communication method, and relates to, for example, a method for carrying out short-distance communication (secret communication) among a plurality of radio communication apparatuses.
2. Related Art
The method described in Japanese Patent No. 3669293 is known as a method for initial setting (authentication procedure or the like) for a plurality of radio communication apparatuses. According to the method described in Japanese Patent No. 3669293, when portable devices fall under the realm of radio wave thereof each other, that is, move closer to a predetermined distance from each other, both devices authenticate each other automatically or with users' confirmations. This can reduce complicated processes such as entries of ID numbers and passwords in an authentication procedure with the portable devices.
On the other hand, the method described in JP-A 2006-60470 (Kokai) is also known as an initial setting method for a plurality of radio communication devices. JP-A 2006-60470 (Kokai) discloses an initial setting method when there are a plurality of portable devices, but the user needs to know a device for reporting setting information and a device for receiving the report before operating the devices.
According to the above-described method of Japanese Patent No. 3669293, when automatic authentication is permitted while the radio communication apparatuses (portable devices) are not so close to each other, there is an increased risk that authentication information may be eavesdropped, which causes security problems. Furthermore, when an authentication button is depressed after the radio communication apparatuses approach each other, there may be a problem that it is difficult to depress the authentication button depending on the position where the authentication button is placed. Therefore, Japanese Patent No. 3669293 also presents the method of depressing the authentication button before approaching and starting automatic authentication when the apparatuses approach each other. According to this method, a detector for detecting that the radio communication apparatuses approach each other (that is, the distance from other party apparatus) is additionally mounted and transmits authentication information when the approach is detected. Although this can solve operability-related problems, the security depends on the accuracy of detecting the approach to a great extent and there still remains a problem that automatic authentication may be performed even when the radio communication apparatuses are not so close to each other.
Furthermore, another problem of the method according to Japanese Patent No. 3669293 is that it is a method for proceeding authentication between two portable devices and when an attempt is made to additionally authenticate another portable device against two portable devices which have already completed authentication, the initial setting procedure becomes complicated. When, for example, an attempt is made to authenticate a portable device C against a set of portable device A and portable device B, which have already completed the authentication procedure to enable three-party communication, the portable device C needs to perform mutual authentication against the portable device A and portable device B separately. This means that if the number of portable devices is N, authentication needs to be performed after making the portable devices approach C(N, 2)=N×(N−1)/(2×1) times. Therefore, the procedure for initial setting becomes more troublesome as the number of portable devices increase. For example, when initial setting is performed on five portable devices, ten approaches are required.